Table 2. Quality assessment of the randomized controlled studies based on the Cochrane Risk of Bias Tool.
| Author | Year | Sequence generation | Allocation concealment | Blinding of participants, personnel and outcome | Incomplete outcome data | Selective outcome reporting | Other sources of bias |
|---|---|---|---|---|---|---|---|
| Lau et al. (42) | 1996 | + | + | ? | − | + | + |
| Lau et al. (43) | 1998 | + | ? | ? | ? | + | + |
| Siu et al. (44) | 2002 | + | + | − | + | + | + |
| Bertleff et al. (45) | 2009 | + | + | − | + | + | + |
| Schietroma et al. (46) | 2013 | + | + | ? | + | + | + |
+: Low risk of bias?: Unclear −: High risk of bias.